Morphological diversity and widespread hybridization in the genus Bythotrephes leydig, 1860 (Branchiopoda, Onychopoda, Cercopagidae)

Morphological variation in the genus Bythotrephes was studied. We analyzed samples from 29 locations through the generic range. Based on the core body length and the total length, as well as several other morphological characters, differences were found that are consistent across five groups of populations previously described as a separate species (B. cederstroemii, B. crassicaudus, B. transcaucasicus, B. brevimanus, and B. longimanus). Individuals with intermediate morphological characteristics were detected where B. cederstroemii, B. brevimanus and B. crassicaudus have geographic overlap. Based on allozyme analysis, hybrids of B. cederstroemii and B. brevimanus were revealed in the zone of contact of these two species in the Volga River drainage and northwestern Russia. nema